Active electrical lighting using neon tubes became popular in the 1920's and developed into a "pop" art form in the United States. Neon lighting became widely used for advertising and sign display. Its brightness and variable color could be relied upon to attract attention. However there are now a number of disadvantages associated with active electrical neon lighting. Such active electrical lighting has fallen out of favor and is banned or closely controlled by zoning and sign ordinances in many towns, municipalities and cities. Second, there are limitations on the complexity of alphanumeric and graphic sign displays inherent in using neon tubes. Neon tubes place a limitation on the configurations that can be achieved. Finally, an active electrical power supply is always required to cause light discharge from the neon gas confined in the tubes.
In the field of passive plastic sign displays, the Prosser et al. U.S. Pat. No. 3,578,538 describes laminated indicator plaques in which a relatively thick opaque white PVC layer is laminated over a transparent PVC layer. The opaque white and transparent or translucent PVC layers are substantially the same thickness. Additional layers are formed over the opaque white layer for example a gray or black matt ink layer and a protective polyurethane lacquer layer. The overall thickness of the opaque white PVC layer and outer layers is greater than the thickness of the transparent or translucent layer.
Indicia are formed in the plaque by engraving indicia that are V-shaped in cross section. The indicia penetrate through the outer layers, namely the protective layer, ink layer, and opaque white layer but only "a little way into the transparent layer". Light from an electro-luminescent panel bonded to the transparent layer or other light source generates light which passes through the small transparent or translucent opening at the base of the V for illuminating the inner walls of the V-shaped cross section indicia. Other coloring material may be applied to the inner walls of the indicia for illumination by light passing through the small light opening at the base of the V.
It is apparent that the purpose of the laminated indicator plaques of Prosser et al. is to provide V-shaped indicia formed primarily through opaque materials. The primary appearance of the sign display is therefore imparted by the opaque surfaces of the inside of the V-shaped cross section of the indicia. The only purpose of the small penetration at the base of the V into the transparent or translucent layer is to-permit passage of light for illuminating the opaque surfaces of the insides of the grooves. As explained at column 2, lines 58-64 of the Prosser et al. patent, the penetration into the translucent or transparent layer forms only a very small fraction of the cross sectional width of the indicia namely 1/31 of the width of the indicia. To this end the V-shaped cross section grooves forming the indicia penetrate only a very small fraction of the thickness of the translucent layer. Thus the sign of Prosser et al. is basically an opaque surface sign and the limited back lighting through the apex of the V-shaped cross section angle is intended only to illuminate the opaque surfaces.
The Brand U.S. Pat. No. 3,226,865 describes another passive plastic sign structure. According to Brand an opaque material is applied across the back side of a transparent sheet. Indicia in the form of trapezoidal cross section recesses are formed through the opaque material extending into the transparent layer. A mirror or other reflective surface is then applied across and over the recesses for forward reflection of light through the recesses to the uncoated side of the transparent layer which forms the viewing side of the sign. Thus Brand requires a mirror like surface for illumination of the recesses and for illumination of the sign display.